The gene encoding CBF2 (CBFB) is disrupted by the chromosome 16 inversion [inv(16)(p13q22)], associated with ~12% of acute myeloid leukemia in humans, resulting in a fusion protein containing most of the CBF2 fused to the coiled-coil tail region of smooth muscle myosin heavy chain (SMMHC). The CBF2- SMMHC fusion protein acts as a dominant repressor of CBF function, binding RUNX1 and dysregulating the expression of multiple genes required for normal hematopoiesis. Current treatment utilizing cytotoxic chemotherapy results in 45-65% five year overall survival but only 20% for patients older than 60. These data clearly indicate that targeted therapies that can improve the therapeutic response for inv(16) AML patients is essential. Emerging literature suggests that inability to cure cancers with current therapies may be attributed to a population of so-called cancer stem cells or cancer initiating cells that have long term self-renewal potential and can fully recapitulate tumor phenotype at time of relapse. Our hypothesis is that small molecules that inhibit the interaction of CBF2-SMMHC with the Runt domain of RUNX1 could be effective therapeutic drugs that induce apoptosis and/or differentiation and eradicate the leukemia initiating cell population, thereby achieving better long term survival. We have identified an initial lead that inhibits the protein-protein interaction between CBF2-SMMHC and RUNX1. We are proposing to further optimize the potency of this lead using structure-based drug design and medicinal chemistry approaches. Compounds will be tested for their ability to relieve CBF2-SMMHC mediated repression and affect the growth, apoptosis, and differentiation of leukemia cell lines. Selected compounds will be tested in vivo in a well-characterized mouse model of inv(16) leukemia. It is possible that inhibiting both CBF2 and CBF2-SMMHC function, as the inhibitors proposed in Aim 1 will do, could result in toxicity or a lack of efficacy, therefore we are proposing to develop small molecule inhibitors which are selective for CBF2-SMMHC over CBF2. Compounds will be tested for their ability to relieve CBF2-SMMHC mediated repression and affect the growth, apoptosis, and differentiation of leukemia cell lines. Selected compounds will be tested in vivo in a well-characterized mouse model of inv(16) leukemia. We hypothesize that effective inhibitors should specifically affect differentiation and cell death of pre- leukemic progenitor cells expressing CBF2-SMMHC with minimal alteration of the normal stem and early progenitor cells in the bone marrow. We propose to study the effect of selected compounds in vivo in normal hematopoiesis. Compounds with minimal or no effect on normal hematopoiesis will be prioritized to study their effect on the reduction/eradication of pre-leukemic progenitors in knock-in mice expressing CBF2-SMMHC.